/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with this
* work for additional information regarding copyright ownership. The ASF
* licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package org.apache.hadoop.zebra.mapred;
import java.io.Closeable;
import java.io.IOException;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.zebra.io.TableScanner;
import org.apache.hadoop.zebra.types.Projection;
import org.apache.hadoop.zebra.schema.Schema;
import org.apache.hadoop.zebra.types.TypesUtils;
import org.apache.pig.data.Tuple;
/**
* Utility class for those interested in writing their own TableExpr classes.
* This class encapsulates a regular table scanner and changes the way how keys
* and rows are accessed (with an internal cache).
*/
final class CachedTableScanner implements Closeable {
private BytesWritable key;
private Tuple row;
private boolean keyReady;
private boolean rowReady;
private int index;
private TableScanner scanner;
/**
* Constructor
*
* @param scanner
* The scanner to be encapsulated
* @throws IOException
*/
public CachedTableScanner(TableScanner scanner, int index) throws IOException {
key = new BytesWritable();
row = TypesUtils.createTuple(Projection.getNumColumns(scanner.getProjection()));
keyReady = false;
rowReady = false;
this.index = index;
this.scanner = scanner;
}
/**
* Get the key at cursor.
*
* @return The key at cursor
* @throws IOException
*/
public BytesWritable getKey() throws IOException {
if (!keyReady) {
scanner.getKey(key);
keyReady = true;
}
return key;
}
/**
* Get the value (Tuple) at cursor.
*
* @return the value at cursor.
* @throws IOException
*/
public Tuple getValue() throws IOException {
if (!rowReady) {
scanner.getValue(row);
rowReady = true;
}
return row;
}
/**
* Get the table index in a union
*
* @return the table index in union
*/
public int getIndex() {
return index;
}
/**
* Seek to a row whose key is greater than or equal to the input key.
*
* @param inKey
* the input key.
* @return true if an exact matching key is found. false otherwise.
* @throws IOException
*/
public boolean seekTo(BytesWritable inKey) throws IOException {
boolean ret = scanner.seekTo(inKey);
reset();
return ret;
}
/**
* Advance the cursor.
*
* @return whether the cursor actually moves.
* @throws IOException
*/
public boolean advance() throws IOException {
boolean ret = scanner.advance();
reset();
return ret;
}
private void reset() throws IOException {
row = TypesUtils.createTuple(Projection.getNumColumns(scanner.getProjection()));
keyReady = false;
rowReady = false;
}
/**
* Is cursor at end?
*
* @return Whether cursor is at the end.
* @throws IOException
*/
public boolean atEnd() throws IOException {
return scanner.atEnd();
}
/**
* Get the schema of the tuples returned from this scanner.
*
* @return The schema of the tuples returned from this scanner.
*/
public String getProjection() {
return scanner.getProjection();
}
/**
* Get the projected schema
* @return The projected schema
*/
public Schema getSchema() {
return scanner.getSchema();
}
/**
* Seek to the end of the scanner.
*
* @throws IOException
*/
public void seekToEnd() throws IOException {
reset();
scanner.seekToEnd();
}
/**
* Close the scanner, release all resources.
*/
@Override
public void close() throws IOException {
scanner.close();
}
}